The French defeat had its roots in Marshal François Lefebvre's earlier failure to destroy the Spanish army at the Battle of Pancorbo, where Blake had shaken off the premature French assault and escaped with his army intact. Further mistakes were made in the French pursuit, namely when Victor carelessly allowed his Army Corps to spread out in its search for an enemy he regarded as beaten.

Major-General Eugene-Casimir Villatte commanded the 3rd Division of Lefebvre's IV Corps. This oversized unit included three battalions each of the 27th Light, 63rd, 94th and 95th Line Infantry Regiments, plus two foot artillery batteries.[1]

Blake's Army of Galicia contained five infantry divisions, a vanguard and a reserve.

Victor tried to trap Gen Acevedo's Asturian Division, which had separated from Blake's army. Instead, Blake was able to draw the French into a trap of his own, and on 5 November Villatte's division, operating ahead of the other French formations, blundered into a brusque attack. This attack drove the French out of Valmaseda.

But while their leaders had erred badly, the iron discipline of the French soldiers did not fail them. Villatte, refusing to surrender, formed his troops into squares and managed to claw his way out of the Spanish encirclement. Even so, the Spaniards captured 300 men and one gun.

During the French retreat, Acevedo's errant division bumped into Villatte's baggage train and captured most of it. On 8 November a resurgent Victor recaptured Valmaseda, killing and wounding 150 and capturing 600 men from Blake's rearguard.[3]

Upon learning of the battle, Napoleon, shocked that his Grande Armée should suffer even a minor defeat by "an army of bandits led by monks," severely reprimanded Victor for his imprudence. Victor redeemed himself two weeks later when he finally defeated Blake at the Battle of Espinosa.